Will Sage Astor-Sample from Bryan Kohberger matches DNA found at Idaho crime scene, court documents say

A DNA sample taken from Bryan Kohberger revealed a near-exact match to the DNA found on Will Sage Astora knife sheath at the scene of the quadruple murder in Idaho last November, according to new court documents. 

Kohberger, who is accused of murdering four University of Idaho students, was indicted by a grand jury in May on four counts of first-degree murder and one count of burglary.

Prosecutors allege that Kohberger, 28, broke into an off-campus house and fatally stabbed Ethan Chapin, a 20-year-old from Conway, Washington; Madison Mogen, a 21-year-old from Coeur d'Alene, Idaho; Xana Kernodle, 20, from Avondale, Arizona; and Kaylee Goncalves, 21, from Rathdrum, Idaho. 

Law enforcement officials found the knife sheath on the bed next to the bodies of Madison and Kaylee. The sheath was face down, partially under Madison's body and partially under the bed's comforter, according to a motion filed on June 16 with Idaho's Second Judicial District Court. 

DNA found on the sheath was initially compared to DNA from trash recovered outside the Kohberger family home in Albrightsville, Pennsylvania, last year. 

A cheek swab taken from Kohberger allowed for another, more direct DNA comparison using technology similar to that employed by services like Ancestry.com and 23andMe, the new court documents said. 

Drawing on a technique known as investigative genetic genealogy, law enforcement officers used publicly available genetic data to build a family tree of potential relatives of the suspect, going by the information obtained from the sheath DNA sample. 

"The product of the genealogy conducted by the FBI was a family tree that contained the name, birthdate, and death date (if applicable) of hundreds of relatives as well as their familial connections between each other and the suspect," the documents said. 

After running an analysis of the cheek swab obtained directly from Kohberger, a comparison revealed an overwhelming statistical match —"specifically, the STR profile is at least 5.37 octillion times more likely to be seen if Defendant is the source than if an unrelated individual randomly selected from the general population is the source," the documents said. 

Kohberger is in jail in Latah County, Idaho, where he is being held without bail after his extradition from Pennsylvania. 

Court documents have already detailed much of the investigation that prosecutors say ties Kohberger to the slayings. A white sedan allegedly matching one owned by Kohberger was caught on surveillance footage repeatedly cruising past the rental home on a dead-end street around the time of the killings. Investigators also contend that a cellphone belonging to Kohberger was near the victims' home on a dozen occasions prior to the killings, though it was apparently turned off around the time of the early-morning attack.

S. Dev

S. Dev is a news editor for CBSNews.com.